edlld by WALTER A. WOLF Eisenhower College Seneca Falls, New York 13148
The Heat of Combustion of Cereals G a r y G. Glachino State University of New York Geneseo, N Y 14454 One of the more nonular . . exneriments in the lahoratorvfor our non-science rni~jors'rhemistry course is the determination ,,i tht. heat of ambustion nf a cornrnerrial breakfast cereal. The experiment does an excellent job of illustrating some .thermochemical concepts. demonstrating exactly what a calorie is (and the factthat food caloriesare act"al1y kilocalories), and the student sees for himself how at least one of those numbers on the box is obtained. Hess's law is illustrated by pointing out that as long as the body "burns" the food to the same final products, the same energy will be obtainedeven though the body obviously receives these products by a different oath. Since it is rlearlg not possihle to provide each student (or pair) witho bornbcalorimrter, theinstruct~~doesrheactual manipulations, while the students help rollect and/or record tho data. Althourh the desired precision does nor really wnrrant it, the procedure normalliused in a physical chemistry laboratory is followed, including the plotting of temperature versus time curves. In this way the students see the correct procedure and gain additional practice in the use of graphs. In preliminary experiments it was found that some cereals were difficult to press into pellets. We have had good success with cocoa cereals such as Cocoa Pehhlesa and Cocoa Crispiesa. Even here, however, the pellets are fragile and must be handled with care. The use of children's cereal undoubtedly also helps students remember the experiment. The results have generally been consistent with the data found on the boxes. Because of student interest it is believed that more is learned here than in conventional calorimetry experiments-even though the instructor must actually do the work. An additional benefit is that many students seemed surprised when it was confirmed that only some water and residue from the fuse wire are visihle in the bomb after ignition.
Qualitative Analysis of the Halogens Joseph J. Spadaro, Jr. North Country Community College Saranac Lake, NY 12983 Concern about lahoratorv.safetv, narticularlv the use of toxic solvents in the under&adua&'lahoratory, has recently received the attention it deserves. This concern has encour-
372 1 Journal of Chemical Education
aced the search for safe. effective alternative solvents "We have developed aprocedure for the qualitative determination of the halogens in the presence of each other. We have found that hexane is asafe and effective replacement for the carbon tetrachloride normally used in this sequence. A brief description of the procedure is as follows: Iodide ion is selectively oxidized to iodine (NaNOz/Hf) andseparated from unmidized bromide and chloride ions uia extraction with hexane. Bromide, remaining in the aqueous solution, is then selectively oxidized to Bromine (KMNO&+) and is also separated from Chloride ion uio hexane extraction. The residual aqueous solution is then tested for chloride in the usual manner using AgNOs salution.
A complete description of these procedures, including suggestions for unknowns, will be furnished upon request.
Transparent Soap J o h n W. Hill and Cynthia S. Hill Transparent soaps are rather popular and often quite expensive. We have developed a cheap and easv . way . to make these attractive and useful products. A typical procedure is given here. Weigh out 20 g of soap flakes such as Ivory Snofl-do not use a synthetic detergent-in a 250-ml beaker. Add 25 ml elvcerol. 15ml95%ethanol. and 15ml of distilled water. Heat gently on a hot plate or water bath (no open flarnes),with occasional gentle stirring, until a clear solution is obtained. Allow to cool to room temperature (or cool quickly in an ice bath) to cause the soan to harden. For colored soap, add one drop of food coloring. Unlike ordinarv soap IJ. CHEM. EDUC., 55.516 (1978)l. the transparent soap, &h its high water, glycerol, &d alcohol content, is readily colored by these water soluble dyes. To perfume the soap, add about 0.5 ml of eugenol (oil of cloves). This mimics the odor of a highly popular and expensive commercial brand of transparent soap. For other fragrances, you can substitute lemon oil, lime oil, or other perfume oil. For storage, the transparent soaps should be wrapped or otherwise enclosed to prevent evaporation of alcohol and water. Keep out of the reach of children; these soaps look a lot like gelatin desserts-they look good enough to eat.
